1. Field of the Invention
The present invention relates to a resist film developing method and, more particularly, to a method of developing a resist film in a desired pattern in fabricating an electronic device by a photolithographic process, and an apparatus for carrying out the same.
2. Description of the Prior Art
As is generally known, photolithography employing a resist film is applied to fabricating an electronic device, such as a semiconductor device. A puddle developing process is employed in developing an exposed resist film by photolithography. As shown in FIG. 1a and 1b, in developing an exposed resist film 1a formed on a work 1, such as a semiconductor wafer, by a photolithographic process, the work 1 is mounted on a support 2, such as a wafer chuck, supported in a developing cup 11, a developer 3 is spread by a nozzle 30 or the like over the surface of the resist film 1a so that the developer 3 is retained in a puddle by surface tension over the surface of the resist film 1a as shown in FIG. 1b to develop the resist film 1a. In this specification, retaining a developer in a puddle by surface tension over the surface of a work will be designated as "puddling" and a developing process using a developer puddle formed by puddling will be designated as "a puddle developing process".
It is well known that developing speed is dependent on the temperature of the developer, and developing speed affects the width of the component lines of the resist film. (Proceedings of Oyo Butsuri Gakkai, Spring, 1989, 2a-K-2, Proceedings of Oyo Butsuri Gakkai, Autumn, 1989, 29-p-L-10).
The prior art photolithography assumes that the temperature of the developer does not change during development because the developer is retained in a puddle of a thickness on the order of several millimeters on the work and hence the .heat capacity of the puddle of the developer is large. Accordingly, the prior art photolithography regulates only the temperature of the developer to be sprayed over the work. However, it was found that the temperature of the developer drops about 6.degree. C. during practical development, which is considered to be due mainly to the evaporation of the developer. It was also found that there is difference between the temperature of the developer in the central area of the work and that of the same in the peripheral area of the work. FIG. 2 shows the variation of the temperature of the developer with time in the central area of the work (solid circles) and in the peripheral area of the work (blank circles). As is obvious from FIG. 2, the temperature of the developer drops about 4.degree. C. in 100 sec in both the central and peripheral areas of the work and about 6.degree. C. in 300 to 600 sec in both the central and peripheral areas of the work, the temperature of the developer in the central area of the work and that of the same in the peripheral area of the work are different, and the mode of temperature variation of the developer in the central area of the work and that of the developer in the peripheral area of the work are different. The temperature difference between the developer in the central area of the work and developer in the peripheral area of the work is considered to be attributable to the following reasons that the temperature of the developer in the central area of the work does not drop rapidly because the central area of the work is in contact with the support 2, whereas the temperature of the developer in the peripheral area of the work drops rapidly because there is nothing around the peripheral area of the work. This temperature difference is unavoidable because the area of the work 1 is greater than that of the supporting surface of the support 2 as shown in FIG. 1b. The support 2 must be smaller than the work 1 to avoid interference between the support 2 and the wafer transporting mechanism to and to suppress wetting the support 2 with the developer to the least extent.
The width of a line of a resist film sensitive to temperature variation is smaller when the temperature of the developer is lower. FIG. 3a shows the width of a line of a resist film formed on a work at measuring points 1 to 7 (FIG. 3b) on the surface of the work. In FIG. 3a, curves IIa, IIb and IIc indicate the dependence of the width of lines on position on the work for resist films (FH-EX, Fuji Hunt Co.) developed by prior art developing processes, respectively. There is a tendency for the width to decrease from a portion of the line in the central area of the work toward a portion of the same in the peripheral area of the work. The difference in width between a portion of the line in the central area of the work and a portion of the same in the peripheral area of the work is in the range of about 0.04 .mu.m to about 0.05 .mu.m.
A resist for excimer laser lithography, which is capable of effectively coping with the miniaturization of semiconductor devices and with the increase of degree of integration large-scale integrated circuits, is one of the resists sensitive to the temperature variation of the developer. Therefore, it is important to solve the foregoing problems in developing a resist film.
The foregoing problems may be solved by supporting a work 1 on a support 2 of a size equal to or greater than that of the work 1 so that the work is entirely in contact with the support 2 as shown in FIG. 4. However, this resist film developing method is not necessarily able to eliminate the influence of the support 2 on the temperature variation of the developer retained on the work 1 and local temperature difference in the developer retained on the work 1 and is not a drastic means for solving such problems. Furthermore, such a large support, as compared with the work, places restrictions on the design of the work transporting system and is liable to be wetted with the developer, and hence the employment of such a large support is not practically disadvantageous.